View
7
Download
0
Category
Preview:
Citation preview
Mark Ritenour
Water Sanitation using
Chlorine
Common Sanitizers
• Chlorine is the most widely used in fresh
fruit & vegetable operations
• Chlorine dioxide (‘Sanova’, ‘Oxine’, etc.)
• Peroxyacetic acid (‘Tsunami’) - less
affected by organic load & pH
• Ozone and UV are used to some extent in
fresh-cut operations
• More effective treating clear water
Benefits of Chlorination
• Relatively inexpensive (Cl2 least
expensive)
• Can effectively reduce pathogen
populations
• Reduces the transfer of decay
organisms to healthy fruit
Sources of Chlorine
• Sodium hypochlorite (NaOCl)
• Liquid (5.25, 12.75, or 15%)
• Calcium hypochlorite [Ca(OCl)2]
• Solid (65 or 68%)
• Chlorine gas (Cl2)
• Gas cylinders
Factors Affecting
Chlorine’s Effectiveness
• Water pH
• Chlorine concentration
• Contact time
• Organic matter
• Water temperature
• Type & growth stage of pathogen
Water pH
• Hypochlorite and Cl2 form
hypochlorous acid (HOCl).
• Hypochlorous acid is what kills
pathogens
NaOCl
Ca(OCl)2
Cl2
=> HOCl
High pH
• At high pH, hypochlorous acid converts to
hypochlorite ion (OCl-)
• Hypochlorite ion is relatively ineffective
against pathogens
HOCl H+ + OCl-
0
10
20
30
40
50
60
70
80
90
100
5 6 7 8 9 10
SOLUTION pH
% C
hlo
rin
e i
n A
vail
ab
le F
orm
OC (32F)
20C (68F)
30C (86F)
Adjusting pH
• Recommended pH is between 6.5 & 7.51983 Chemistry & Control of Modern Chlorination - Palin
Chlorine Concentration
• Relatively low chlorine concentrations (<
40 ppm) can kill pathogens
• Higher concentrations are commonly
used to compensate for various losses
• Recommendation: 100 to 150 ppm free
chlorine
Contact Time
• Higher chlorine concentrations kill
microbes faster (e.g. < 1 min)
• Lower chlorine concentrations require
longer exposure time
• More resistant microbes or stages of
growth may require longer exposure
times to kill
Organic Matter
• Organic matter reacts with chlorine and
quickly reduces the amount of chlorine
available to kill microbes
• However, this
chlorine may
still be
measured by
total chlorine
testing kits
Biofilms
• Biofilms are sticky to slimy accumulations of fungi and
bacteria that accumulate and grow on damp or wet
surfaces
• Regular cleaning and sanitizing will prevent their
formation, but cannot penetrate and remove existing
biofilms
• Existing biofilms can only be removed by scrubbing
Temperature
• At higher temperatures
– kills microbes faster
– more rapid loss of chlorine activity
• Temperature differences between
product and water can lead to
internalization
Type and Growth Stage
• Bacteria, and germinating fungal spores
and mycelia are relatively easy to kill with
chlorine
• Quiescent spores are much more
resistant to chlorine
• Microbes inside fruits and vegetables are
protected and will not be killed
Chlorine Recommendations
• Maintain free chlorine levels between
100 to 150 parts per million
• Maintain pH between 6.5 and 7.5
• Drain tanks often (e.g., daily) and refill
with clean water
• Use self-cleaning screens in dump
tanks to remove large debris and
organic matter
Maintaining
Adequate Chlorination
• Manual monitoring and addition of chlorine
• Requires frequent monitoring of chlorine
concentrations and pH
• Automated chlorine dispensing
• Timed release or based on measured chlorine
concentrations or ORP
• With or without automatic pH adjustments
Chlorine Test Kits
• Use kits that measure free chlorine
levels
• Total chlorine kits can measure both free
and bound chlorine
• If sample dilution is required, dilute with
distilled water
Chlorine Recommendations
• Check free chlorine levels often or use
automated systems
• Use all chemicals according to their
labels
• Consult local regulations for disposal of
chlorinated water
Demonstration
• Calculate volume of chlorine (sodium
hypochlorite) needed to give a desired
ppm
• Observes effects of pH and organic
matter on the free chlorine levels in
solution
How much NaOCl to add?
Volume of NaOCl to add
=
Desired ppm of free chlorine X total tank volume
(% NaOCl in concentrate) X 10,000
Example
• Using 5.25 % NaOCl
• Desire 100 ppm Cl solution
• Total solution volume 500 gallons
Example
Volume of NaOCl to add
=
100 ppm of free chlorine X 500 gallons
5.25% NaOCl X 10,000
= 0.95 gallons
How much NaOCl to add?
• Add 0.95 gallons of 5.25% NaOCl
solution to 499 gallons of water
Effects of pH and Organic
Matter on Free Chlorine Levels
• De-ionized water
only
Effects of pH and Organic
Matter on Free Chlorine Levels
• De-ionized water
with 0.95 ml of
5.25% NaOCl
solution
• What form is the
NaOCl in?
Effects of pH and Organic
Matter on Free Chlorine Levels
• De-ionized water
with 0.95 ml of
5.25% NaOCl
solution
• pH adjusted to
7.5
• What form is the
chlorine in now?
Effects of pH and Organic
Matter on Free Chlorine Levels
• De-ionized water
with 0.95 ml of
5.25% NaOCl
solution
• pH adjusted to
7.5
• Then tomato
juice added
Thank You!• For more information,
visit the UF Postharvest Website
http://irrec.ifas.ufl.edu/postharvest/
Recommended